The aircraft was maintained in accordance with existing regulations, and there were no defects reported before the occurrence flight. The pilot was certified and experienced for the flight. It was determined that at least 17 of the third-stage compressor wheel blades had progressive cracks. One of these cracks progressed to a point where the blade failed under normal operating loads. The damage to the fourth-stage compressor wheel was consistent with overstress damage caused by the liberation of the third-stage compressor blades. Therefore, this analysis will focus on the failure of the third-stage compressor wheel and the subsequent hard landing and rollover. Although the third-stage compressor wheel was original to the engine, it was well within the total life time limits of hours and cycles, and the overhaul was done within the prescribed time frame. During the last overhaul of the third-stage compressor wheel, there were no noted discrepancies or defects. The 17 compressor blades that failed due to a progressive type of failure were covered in oxidation from the post-crash fire; therefore, a propagation rate could not be determined. However, if the fatigue cracks were present during the last overhaul, it would be reasonable to assume that they would have been noticed during the FPI of the third-stage wheel. Therefore, it is likely that the progressive failure developed at some point after the last overhaul. Metallurgical examination could not determine the initiating event that led to the progressive cracks on a number of the third-stage compressor blade roots. However, when a progressive failure crack reaches a critical size, the remaining blade section fails due to overstress at normal operating loads. It is likely that the third-stage compressor wheel experienced this type of blade failure, causing destruction of the third- and fourth-stage compressor wheels. The engine power loss occurred while the helicopter was flying over rugged terrain, which was not suitable for landing. Stretching the glide in an attempt to reach a suitable landing area resulted in a loss of main rotor rpm, which subsequently resulted in a hard landing. The following TSB Engineering Laboratory report was completed: LP 062/2006 - Engine Teardown and Examination Bell 206L, C-GSMZ This report is available from the Transportation Safety Board of Canada upon request.Analysis The aircraft was maintained in accordance with existing regulations, and there were no defects reported before the occurrence flight. The pilot was certified and experienced for the flight. It was determined that at least 17 of the third-stage compressor wheel blades had progressive cracks. One of these cracks progressed to a point where the blade failed under normal operating loads. The damage to the fourth-stage compressor wheel was consistent with overstress damage caused by the liberation of the third-stage compressor blades. Therefore, this analysis will focus on the failure of the third-stage compressor wheel and the subsequent hard landing and rollover. Although the third-stage compressor wheel was original to the engine, it was well within the total life time limits of hours and cycles, and the overhaul was done within the prescribed time frame. During the last overhaul of the third-stage compressor wheel, there were no noted discrepancies or defects. The 17 compressor blades that failed due to a progressive type of failure were covered in oxidation from the post-crash fire; therefore, a propagation rate could not be determined. However, if the fatigue cracks were present during the last overhaul, it would be reasonable to assume that they would have been noticed during the FPI of the third-stage wheel. Therefore, it is likely that the progressive failure developed at some point after the last overhaul. Metallurgical examination could not determine the initiating event that led to the progressive cracks on a number of the third-stage compressor blade roots. However, when a progressive failure crack reaches a critical size, the remaining blade section fails due to overstress at normal operating loads. It is likely that the third-stage compressor wheel experienced this type of blade failure, causing destruction of the third- and fourth-stage compressor wheels. The engine power loss occurred while the helicopter was flying over rugged terrain, which was not suitable for landing. Stretching the glide in an attempt to reach a suitable landing area resulted in a loss of main rotor rpm, which subsequently resulted in a hard landing. The following TSB Engineering Laboratory report was completed: LP 062/2006 - Engine Teardown and Examination Bell 206L, C-GSMZ This report is available from the Transportation Safety Board of Canada upon request. The engine power loss event was a result of the failure of the third-stage compressor wheel. Numerous blades on the third-stage compressor wheel had progressive cracks, which had propagated through approximately 50percent of the blade thickness. The liberated compressor blades caused severe internal damage to the third- and fourth-stage compressor wheels.Findings as to Causes and Contributing Factors The engine power loss event was a result of the failure of the third-stage compressor wheel. Numerous blades on the third-stage compressor wheel had progressive cracks, which had propagated through approximately 50percent of the blade thickness. The liberated compressor blades caused severe internal damage to the third- and fourth-stage compressor wheels. The glide of the helicopter was extended to avoid landing in a wooded area. However, depleting some of the main rotor rpm to extend the glide presents the risk that there may be insufficient rpm available for a safe autorotation and landing.Finding as to Risk The glide of the helicopter was extended to avoid landing in a wooded area. However, depleting some of the main rotor rpm to extend the glide presents the risk that there may be insufficient rpm available for a safe autorotation and landing. On 31May2007, the TSB released Aviation Safety Information Letter A06W0182-D1-L1. The letter outlines two other recent occurrences involving Allison/Rolls-Royce 250-C20R turbo-shaft engines and the similar mode of failure of the third-stage compressor wheel. On 05October2006, a Bell B206L, operated by Great Slave Helicopters Ltd., registration C-GHBY, was on approach to a remote landing site when the engine (Allison/Rolls-Royce 250-C20R, serial number CAE-295218) flamed out. A hard landing ensued and the helicopter was substantially damaged when the main rotor severed the tail boom. One passenger sustained a minor injury. The pilot and three other passengers were uninjured. Detailed examination of the engine determined that a third-stage compressor blade had liberated from the third-stage compressor wheel, part number 23032623, due to high cycle fatigue cracking. Fatigue cracks were evident on 11 of the 29blades on the wheel. All of the fatigue failures showed initiation around the mid-chord on the convex (compression) side of the blade and the fatigue cracks had multiple initiation sites. The reason for the fatigue cracking has not been determined. On 10April2006, a McDonnell Douglas MD520N helicopter, powered by an Allison/Rolls-Royce 250-C20R engine, serial number CAE-295415, was involved in a power loss event near Gmund, Austria. The extent of injuries and damage is unknown. Examination by the engine manufacturer determined that the engine had lost power due to a third-stage compressor blade failure, and that the general fracture morphology in the failed third-stage airfoil was consistent with fatigue progression. On 10April2006, a McDonnell Douglas MD520N helicopter, powered by an Allison/Rolls-Royce 250-C20R engine, serial number CAE-295415, was involved in a power loss event near Gmund, Austria. The extent of injuries and damage is unknown. Examination by the engine manufacturer determined that the engine had lost power due to a third-stage compressor blade failure, and that the general fracture morphology in the failed third-stage airfoil was consistent with fatigue progression. There are approximately 979 Allison/Rolls-Royce 250-C20R engines in service, and several Canadian helicopter operators currently use Allison/Rolls-Royce 250-C20R engines in their fleets. Rolls-Royce has recently achieved Federal Aviation Administration (FAA) certification of new and improved compressor wheels for the model 250-C20R turbo-shaft engine. The new wheels are manufactured from machined wrought stock rather than from cast stock. There is no evidence to indicate that the improved compressor wheels are a response to the recent compressor blade failures; however, the new design is expected to increase longevity and reduce operating costs, and may provide better fatigue performance compared to the cast wheels. In its response to the Aviation Safety Information Letter, Transport Canada stated that it was drafting an Airworthiness Directive that will address this issue in Bell Helicopter Textron Canada (BHTC) model 206B series helicopters.Safety Action Taken On 31May2007, the TSB released Aviation Safety Information Letter A06W0182-D1-L1. The letter outlines two other recent occurrences involving Allison/Rolls-Royce 250-C20R turbo-shaft engines and the similar mode of failure of the third-stage compressor wheel. On 05October2006, a Bell B206L, operated by Great Slave Helicopters Ltd., registration C-GHBY, was on approach to a remote landing site when the engine (Allison/Rolls-Royce 250-C20R, serial number CAE-295218) flamed out. A hard landing ensued and the helicopter was substantially damaged when the main rotor severed the tail boom. One passenger sustained a minor injury. The pilot and three other passengers were uninjured. Detailed examination of the engine determined that a third-stage compressor blade had liberated from the third-stage compressor wheel, part number 23032623, due to high cycle fatigue cracking. Fatigue cracks were evident on 11 of the 29blades on the wheel. All of the fatigue failures showed initiation around the mid-chord on the convex (compression) side of the blade and the fatigue cracks had multiple initiation sites. The reason for the fatigue cracking has not been determined. On 10April2006, a McDonnell Douglas MD520N helicopter, powered by an Allison/Rolls-Royce 250-C20R engine, serial number CAE-295415, was involved in a power loss event near Gmund, Austria. The extent of injuries and damage is unknown. Examination by the engine manufacturer determined that the engine had lost power due to a third-stage compressor blade failure, and that the general fracture morphology in the failed third-stage airfoil was consistent with fatigue progression. On 10April2006, a McDonnell Douglas MD520N helicopter, powered by an Allison/Rolls-Royce 250-C20R engine, serial number CAE-295415, was involved in a power loss event near Gmund, Austria. The extent of injuries and damage is unknown. Examination by the engine manufacturer determined that the engine had lost power due to a third-stage compressor blade failure, and that the general fracture morphology in the failed third-stage airfoil was consistent with fatigue progression. There are approximately 979 Allison/Rolls-Royce 250-C20R engines in service, and several Canadian helicopter operators currently use Allison/Rolls-Royce 250-C20R engines in their fleets. Rolls-Royce has recently achieved Federal Aviation Administration (FAA) certification of new and improved compressor wheels for the model 250-C20R turbo-shaft engine. The new wheels are manufactured from machined wrought stock rather than from cast stock. There is no evidence to indicate that the improved compressor wheels are a response to the recent compressor blade failures; however, the new design is expected to increase longevity and reduce operating costs, and may provide better fatigue performance compared to the cast wheels. In its response to the Aviation Safety Information Letter, Transport Canada stated that it was drafting an Airworthiness Directive that will address this issue in Bell Helicopter Textron Canada (BHTC) model 206B series helicopters. The TSB is concerned about the number of recent failures of third-stage compressor blades on Allison/Rolls-Royce 250-C20R engines due to fatigue cracking, with no determination as to why the fatigue cracking is occurring. Failure of third-stage compressor blades will trigger an in-flight loss of engine power, which can result in substantial damage to the helicopter and death or serious injury to the occupants.Safety Concern The TSB is concerned about the number of recent failures of third-stage compressor blades on Allison/Rolls-Royce 250-C20R engines due to fatigue cracking, with no determination as to why the fatigue cracking is occurring. Failure of third-stage compressor blades will trigger an in-flight loss of engine power, which can result in substantial damage to the helicopter and death or serious injury to the occupants.